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Reserve: Which Clock Is Running While You Wait for the Phone

§117.21 divides reserve into three flavors, and each burns a different clock. Assignments that ignore the difference are the most common Part 117 scheduling violation.

Airport/standby reserve = FDP

If the company requires you at the airport, every minute of it is part of your flight duty period (§117.21(b)) — it picks a Table B column like any other duty, and the whole stretch counts.

Short-call reserve: the 16-hour wall

A reserve availability period (RAP) may not exceed 14 hours. For an unaugmented assignment, FDP + RAP measured from the start of the RAP may not exceed the lesser of Table B + 4 hours, or 16 hours (§117.21(c)(3)). For augmented crews it is Table C + 4 (§117.21(c)(4)). A 4-hour RAP after a midday report therefore cannot support a full 14-hour FDP.

Extensions under §117.19(a)(1) reach this combination too — the same +2 h — but the once-per-rest-cycle and cumulative-cap limits still apply.

Long-call reserve: the 12-hour heads-up

If the assignment would begin before and operate into the window of circadian low (0200–0559 home-base time), you must get 12 hours' notice of report time (§117.21(d)). No 3 a.m. "be at the airport in 90 minutes" calls for a WCL operation.

Switching flavors costs a rest

Long-call to short-call conversions require a §117.25(e) rest first (§117.21(e)) — the company cannot re-designate you mid-rest-cycle to dodge the limits.

What reserve days owe you

The same 10-hour/8-hour rest before the RAP or FDP.
The rolling 30-hour weekly break.
Rest between a completed RAP and the next one (§117.21(c)(2)).

Check an FDP+RAP combination in the free Part 117 calculator.

Verified against eCFR 14 CFR 117.21, 117.25. Educational only.